An SCR system that includes an SCR device is developed as an exhaust gas purification system for purifying NOx contained in exhaust gas of a diesel engine.
In such an SCR system, a urea solution stored in a urea solution tank is supplied to an upstream side of the SCR device in an exhaust gas passage to generate ammonia, and NOx is reduced by this ammonia in the SCR device for purification of the exhaust gas.
The SCR system includes an SCR sensor that has a float urea solution level sensor provided in the urea solution tank. The float urea solution level sensor includes a float that follows the liquid surface of the urea solution in the urea solution tank, and a detecting unit that detects the position of the float to detect the level of the liquid surface of the urea solution stored in the urea solution tank. Thus, the SCR system can detect a remaining amount of the urea solution.
The liquid surface of the urea solution is not stable while a vehicle is running Therefore, the SCR system is configured to detect the level of the liquid surface of the urea solution while the vehicle is not running (when the key switch is turned on or when the key switch is turned off) in order to accurately measure the level of the liquid surface of the urea solution.
Prior art document information related to the invention of this application includes the following: